1. Field of the Invention
This invention relates to infrared radiation detection and, more particularly, to infrared video cameras and associated processing systems for visualizing gas clouds on a video display.
2. Background Art
There are literally thousands of chemical processes and systems which need continuous monitoring to ensure the safety and health of both site workers and the general populace. It is common for chemicals, either during the manufacturing process or in the bulk distribution thereof, to be stored for long periods of time, moved about an area, transferred from container to container or transported in long pipelines. Unfortunately, it is not uncommon for chemicals to be stored or transported in deteriorating tanks or pipes. The chance of spills and accidental releases of chemicals to the environment seems to rise every day. There is a clear need not only for a range of monitoring techniques to deal with early detection and subsequent tracking of accidental spills or leaks, but also for routine monitoring of chemical plants and storage areas.
Current monitoring techniques become inadequate when gases are involved because of the ability of most gases to travel unseen far past the point of original detection. The wind alone can make the path of release a matter of guess work and even the point of origin a matter of doubt. What is needed is a method in which escaping gases can be made visible to the eye and use the superior ability of human vision to gauge location and general movement. Once visible to the human eye, the gas image can then be subjected to processes of automation, such as machine vision, to aid in the monitoring and detection process.
Considerable effort has been expended in the past in the application of thermal imaging to gas detection. Optical techniques in general, based upon the absorption or emission of infrared radiation by gases and vapor, have been continuously developed for many years. Today, it is possible to use laser and non-laser systems to make precise concentration measurements along beam paths. However, there are few practical systems for obtaining an image of a gas cloud and, hence, for obtaining a real-time representation of the dynamics of the gas cloud.
One present technique for measuring gas is known as backscatter absorbing gas imaging, and uses an infrared video camera, together with a laser, to raster scan and illuminate the scene. The laser beam passes out through the camera optics in the reverse direction to the incoming radiation and the backscatter radiation from the background (terrain, buildings, etc.) behind the gas cloud is detected by the camera. The gas is detected by its absorption relative to the background. These systems offer good sensitivity and signal-to-noise ratios. However, they use a cooled infrared video camera which requires a separate source of cooling, such as a compressor, a bottle of liquified coolant or a thermoelectric cooler to operate. The cooled camera not only adds considerably to the expense of the system, but also increases maintenance and reduces the portability of the system. In addition, there are limitations imposed on the use of lasers, an active element in the system, which severely limits the overall utility of these systems. Only gases which have absorption features coincident with the laser (CO.sub.2, He--Ne, etc.) can be detected. The essential laser also adds to the cost and complexity of the system. Presently, the range of these systems is not very large and, perhaps the biggest disadvantage of all is that the systems cannot image against a sky background. U.S. Pat. No. 4,555,627 shows one arrangement of a backscatter absorbing gas imaging system.
Other systems for detecting gases, chemicals or the like are shown, for example, in U.S. Pat. Nos. 3,563,658; 3,662,171; 3,715,497; 4,227,210, 4,390,785; 4,543,481; 4,670,653; 4,725,733; 4,937,477; 4,963,742; 4,963,744; 4,965,447 and 4,967,276.
It is not uncommon to process the output signals generated by infrared video cameras to enhance the desired signal and remove unwanted noise. The prior art processing has been generally limited to integration and subtraction techniques which limit the high noise levels inherent in infrared video cameras. Integration has classically been used to reduce the quantity of random noise present in the signal. However, the chief failing of integration is that it also prevents the quicker and more transient features of the desired signal from being seen. For example, the edges of gas clouds and the areas subjected to wind may be effectively integrated from the signal. Subtraction of consecutive frames from each other has also been used to separate the moving portions in the image from the stationary portions, using the assumption that the gas cloud moves while the background image does not. A major limitation of subtraction techniques is that often the gas cloud moves so slowly that it, in addition to the background, is removed. Subtraction alone can do nothing to reduce the noise when the noise resembles gas in its ability to change from frame to frame.
The primary difficulty of the prior art techniques is that they are not adequate to separate the signal from the noise in a gas imaging system. A vague image of the gas cloud might be visible after processing, but it is not sufficient to permit accurate and reliable detection, particularly by automatic methods. Accordingly, it is an object of the present invention to provide enhanced processing techniques on the output of an infrared video camera or the like to provide a better signal-to-noise ratio and a more accurate image of a moving gas cloud.
It is a further object of the present invention to provide a passive, non-laser based, preferably uncooled, infrared video camera detection system for accurately and inexpensively imaging a moving gas cloud.